This application is a national stage of PCT/IB97/01191 filed Oct. 20, 1997 and based upon EP 97/05573.6 filed Apr. 4, 1997 under the International Convention.
This invention relates to a process for the continuous dyeing of warp yarn, particularly cotton warp yarn, with indigo or with other groups of dyestuffs, which after impregnation and squeezing-off, require oxidation or heat treatment for development and fixation.
Continuous warp dying machines for the indigo dyeing of blue denim are known, which consist of connected dyeing vessels disposed in series and comprising a squeezing device, or of padding mangles with a relatively large bath volume. These dyeing vessels or padding mangles are also used for the dyeing of black and colored denim with sulfide or vat dyes. In order to solve color-running problems and in order to achieve an improved dyestuff utilization, it is known that additional units, which consist of a padding mangle with an economizer vat and a subsequent steamer, can be incorporated in warp yarn dyeing machines. These units therefore cannot be used for the main production operation of indigo dyeing.
The known dyeing vessels which comprise a squeezing device or padding mangles, consist of simple roller vats in which the warp to be dyed is impregnated by passing it and deflecting it over a plurality of cylinders or rolls and/or deflection rollers which are located under the level, followed by a squeezing operation. The length of warp under the liquor and thus the residue time in the dye liquor is determined by the number of rolls and deflection rollers under the liquor and their distance from each other. Such a dyeing device is described for instance in EP 0 361 098.
Since the warp speed during indigo dyeing is predetermined and in practice cannot be changed, the time of immersion and the volume of liquor are constant in this case and therefore depend only on the construction of the dyeing vessel.
Greater flexibility is required due to the growing demand for indigo blue materials for jeans with different wash-resistance and different depth of shade, for indigo dyeing of blue or super blue denim, and due to the increasing market share for black and colored denims.
In conventional indigo dyeing installations, for instance different depths of shade require the use of fewer dyeing vessels for lighter hues. Dark hues require a plurality of dyeing vessels disposed in series. Six dyeing vessels each containing up to 2500 l of dyeing liquor, are generally used for a dark shade. This means that conventional indigo dyeing installations have to be reset for the production of different depths of shade. Depending on the desired shade of color, more dyeing vessels have to be used or dyeing vessels have to be eliminated, and dyeing liquors have to be pumped in or pumped off. The dyeing liquor which is not required in the meantime, and which can amount to several thousand liters, has to be drained off or stored for the time being.
In the known loop dye installation, only one dyeing bath is necessary, and the warp yarn band is repeatedly passed therethrough. It is passed through four or five times for dark indigo shades.
In order to reduce their use of dyeing liquor, it has already been proposed to provide a wet dwelling stretch arranged between the immersion bath and the squeezing device, which is arranged in an airtight housing and has an oxygen-poor, respectively oxygen-free atmosphere. Such installations are described for instance in DE OS 43 42 313 and in U.S. Pat. No. 3,981,680.
Shades other than indigo blue are obtained by dyeing with other groups of dyestuffs, mostly sulfide or vat dyes. These and the other groups of cotton dyestuffs, also such as reactive or vat dyestuffs, have different affinities for cotton, which are generally higher than that of indigo. Moreover, their affinities are substantially influenced by the dyeing temperature, which may differ extensively for different groups of dyestuffs. Thus, for example the affinity and dyeing efficiency of indigo increases with decreasing temperature, while for other groups of dyestuffs it mostly increases with increasing temperature.
A higher affinity and dyestuff utilization would be obtained by cooling the indigo dyeing bath in conventional dyeing machines. This is economically disadvantageous, however due to the multiplicity of dyeing vessels and the large amount of dyeing liquor.
Another problem which occurs with the conventional dyeing machines is that the dyestuff is extracted from the dyeing bath due to its affinity. This results in the initial part of the warp yarn band being dyed darker than the end thereof, so that what is termed a head-to-tail progression therefore occurs. This worrying phenomenon, which can manifest itself over several thousand meters of the warp to be dyed, occurs in particular in large installations which contain a large volume of dye bath, and which result in long dyeing runs.
It is an object of the invention therefore to eliminate the disadvantages of conventional processes for the continuous dyeing of warp yarn, particularly cotton warp yarn, with indigo or other groups of dyestuffs when after impregnation and squeezing-off require oxidation or heat treatment for development and fixing. In particular, an object is to achieve a definite reduction in the amount of dyeing liquor required, and to create economically favorable prerequisites for cooling or heating the dyeing liquor. At the same time, an object is to make it possible for the residence time of the warp yarn band in the dyeing installation to be variable using simple structural means, and for the fixing temperature to be selectable from below room temperature to above 100xc2x0 C.
An object of the present invention is, therefore, to provide a process for the continuous dyeing of warp yarn, particularly cotton warp yarn, with indigo or other groups of dyestuffs, which makes a high degree of variability possible when dyeing warp yarns with different color shades, and with different groups of dyestuffs also, and to provide an apparatus which effects dyeing under the optimum conditions in each case when using indigo dye, or sulphide or vat dyes according to choice.
This object is achieved according to the invention by passing a warp yarn band through an air-tight, sealed dyeing reactor which can itself be adjusted to the optimum technological conditions for the respective groups of dyestuffs. For this purpose, the warp yarn band is impregnated in fresh dyeing liquor after an initial immersion and is subsequently squeezed off in an intermediate squeezing device situated in the reactor. Thereafter, the fixing duration is put into effect via guide and deflection rollers with the exclusion of oxygen, with or without repeated immersion in fresh dyeing liquor according to choice, wherein the residence time of the warp threads in the dyeing reactor can be varied corresponding to the desired shade of color and to the technological requirements imposed on the group of dyestuffs concerned.
The dyeing reactor according to the invention is a vessel which is closed at the top and which has openings at its bottom end for the inlet and outlet of the warp yarn band. Vessels for the dyeing liquor, in which the bottom reactor opening is immersed, are disposed under the dyeing reactor. These vessels at the same time form a water lock with guide and deflection rollers which seal the dyeing reactor from the surroundings and by means of which the warp yarn band is fed in and discharged. In addition, a further squeezing device may be disposed in the inlet vat, which squeezes out air which is still contained in the entering warp yarn band. These vessels are equipped with double bottoms by means of which the indigo dyeing liquor can be cooled, or by means of which other dye baths, for example sulphide dyes, can be heated. An intermediate squeezing device is disposed in the dyeing reactor, the squeezing pressure of which can be adjusted in a variable manner down to zero pressure. Instead of the intermediate squeezing device, or in addition thereto, pairs of rollers can be used which strip off excess dyeing liquor when the squeezing device is opened and which thus prevent dyeing liquor from dripping off. The pairs of rollers are adjustable, and are disposed so that the warp yarn band has to follow a more or less pronounced S-shaped curve or a Z-shaped curve. The dwell time of the warp yarn band can be shortened or prolonged, depending on the technological requirements, by guide and deflection rollers which are disposed in the inside of the dyeing reactor and which are vertically displaceable in its interior space.
A hydraulic pipe system for feeding the reactor with dyeing liquors is disposed underneath the dyeing reactor. This circulation system, which consists of feed pipes with pumps disposed therein and of a plurality of valves, is employed for the circulation of the impregnating or dyeing liquor and, when there is a corresponding requirement, for feeding in a feed liquor or higher concentration.